18 LAKAMIE BASIN, WYOMING. 
bed of the Casper and the fractured condition of the next limestone 
bed above that there is at this locality a plane of movement at the 
junction of the sedimentary and the crystalline rocks. 
Section of Casper formation in Plumbago Canyon, Wyoming. 
Red beds. Feet. 
Limestone and shale interbedded 40 
Limestone, heavy bedded 20 
Salmon-colored massive sandstone 40 
Shaly limestone 50 
White limestone , 25 
Shales with limestone interbedded 100 
Limestone 10 
Shaly limestone ■ 20 
Limestone, fractured 20 
Shaly limestone 70 
White fine-grained limestone 30 
Schists. 
In T. 20 N. the base of the Casper formation is faulted out for some 
distance and only 80 feet of limestone remain, overlain by alternations 
of white sandstone and limestone. There is a bed of coarse reddish 
sandstone at the top, overlain by Chugwater red beds. Sandstone 
appears again under the limestone just east of the road crossing in 
T. 21 N. The upper sandstone is a prominent feature in and north 
of T. 23 N. It is spread out widely by the anticline north and north- 
west of Boswell Spring, but is buried under Tertiary deposits for 
some distance in the region west of Garrett. Where it reappears to 
the north it consists of 100 feet of hard sandstone, in large part 
quartzitic, which rises in a line of prominent knolls extending north- 
ward from sec. 18, T. 25 N., R. 74 W., to Marshall. The underlying 
limestone rises in a line of ridges parallel to these knolls ; it is about 
200 feet thick and is separated from the granite and schists by a few 
feet of brown sandstone. 
In the region east of Little Medicine post-office the Casper forma- 
tion consists mostly of limestone lying on a small amount of sand- 
stone and overlain by brown and gray sandstones. In one promi- 
nent ridge near the head of the south prong of Little Medicine Bow 
Creek the lower beds of limestone for 100 feet contain numerous 
cherty layers and are separated from the granite by 30 feet or more 
of red shale merging down into a foot or two of sandstone. These rocks 
strongly suggest the Amsden formation of the Bighorn Mountains, 
which is separated from the Chugwater red beds by the Tensleep 
sandstone. 
Erosion and weathering of limestone slopes. — The monuments and . 
11 mushroom gardens" formed by the erosion of the massive sand- 
stones of the Casper formation have already been mentioned. The 
